1. Field of the Invention
This invention relates to silver halide photographic materials having improved granularity and color saturation. In particular, the invention relates to a photographic element containing at least two separate layers of different sensitivity to green light, including a more active magenta coupler in the more sensitive layer and a less active magenta coupler in the less sensitive layer or layers, wherein one of said magenta couplers is a pyrazolone coupler and the other of said magenta couplers is a pyrazoloazole coupler.
2. Description of Related Art
There is a continuing need in the photographic art to improve and optimize the attributes of the film, such as the image structure of the film. In particular, there is a desire to reduce the amount of "noise," or nonuniformity, in the developed film. The visual sensation produced by such nonuniformity is termed "graininess," while the objective measure of the nonuniformity is termed "granularity." See T. H. James, "The Theory of the Photographic Process," (4th ed. 1977), pp. 618-33). Preferably, reduction in the granularity of the developed film should be achieved without adversely affecting other photographic parameters, such as sensitivity to light (speed), latitude, sharpness, interimage effects, curve shape, D-max, and density.
Various approaches to optimizing granularity are known in the art. Such approaches include: coating high concentrations of silver; reducing the size of grains in the film; and decreasing the full development of grains by the use of development inhibitors. The foregoing methods are not always desirable, however, since they require the coating of additional silver in order to obtain the desired curve shape and density. The use of more silver is additionally disadvantageous since it often results in increased light scattering, which degrades the performance of the underlying layers. Moreover, use of excess silver can result in difficulties in the removal (bleaching) of the silver from the developed film.
Smearing couplers have also been used to reduce granularity. This method, however, often undesirably reduces the film sharpness.
Another approach, use of couplers that generate low extinction dyes, involves the use of more silver, with the accompanying disadvantages discussed above.
Another method, involving coating reduced amounts of couplers in the layers of the photographic element in order to "starve" the coupler, generally has a negative impact on D-max, curve shape, color saturation, and silver efficiency.
Pyrazolone and pyrazoloazole compounds are well known in the art to react with oxidized developer in a photographic system to produce magenta dyes. Both of these classes of compounds are useful as two-equivalent image couplers, that is, couplers having a coupling-off group that is photographically inert and does not serve any additional function such as inhibition, bleach acceleration, color masking and the like.
Photographic elements using only pyrazoloazole compounds as the image coupler can have excellent image structure, particularly granularity, but are deficient in terms of process sensitivity. In particular, small changes in the composition of the processing solutions can result in excessive fluctuations in photographic responses such as contrast. In practice, this leads to unpredictable shifts in overall color balance.
Conversely, photographic elements using only pyrazolone compounds as the image coupler can have excellent process sensitivity, but are deficient in terms of image structure, particularly granularity. This is because pyrazolone couplers do not allow for good coupler "starvation," especially when located in the most light-sensitive layers, a methodology known to reduce overall granularity.
It is known to use combinations of various pyrazolone and pyrazoloazole couplers in the same or different layers of a photographic element, as shown, for example, in U.S. Pat. No. 4,600,668, European patent application EP-A-0 467 327 A1, and Japanese publications 61-273,544 and 62-206544. However, these and other known elements have not proven to be satisfactory, and the known methods of reducing granularity typically have an adverse effect on other film properties.
Accordingly, there is a need for a film that has reduced granularity and the desired high color saturation without adverse impact on other desired photographic parameters such as latitude, sharpness, interimage effects, and total materials laydown for silver, couplers, and other components.